1. Field of the Invention
The present invention generally relates to a two-speed electromagnetic clutch for driving an air conditioning compressor from the internal combustion engine of a bus or a similar vehicle subject to operation at various speeds and conditions such as operation over city streets at relatively low speeds with frequent stops and operation over-the-road at relatively high speeds with infrequent stops. The drive clutch includes two pulleys, one having a larger diameter than the other, a common rotor, concentrically arranged armature discs associated with the rotor for driving engagement therewith when concentrically arranged electromagnetic coils on the opposite side of the rotor attracts one of the armatures into driving engagement with the rotor. Each of the armatures is independently connected to the pulleys so that the rotor may be selectively driven from either the larger diameter or smaller diameter pulley with the structural components and association of these components being unique to provide an efficient two-speed drive clutch which may be easily installed in new construction as well as retrofitted into existing structures.
2. Description of the Prior Art
Electromagnetic drive clutches have been provided for selectively driving air conditioning compressors in vehicles in order to maintain the occupants or passenger space in a vahicle at a comfortable temperature and humidity level. Various patents exist covering such structures with my prior U.S. Pat. Nos. 3,565,223 issued Feb. 23, 1971 and 4,296,851 issued Oct. 27, 1981 being typical of such arrangements with the prior patents cited in the above-mentioned patents also being relevant to this subject matter. However, electromagnetic clutches usually include a single pulley driven by a belt from a power take-off pulley on the internal combustion engine of a vehicle which is adequate for most purposes. However, when a vehicle is driven in congested traffic areas, such as in city driving, the input speed to the compressor is reduced and thus the output of the air conditioning compressor is reduced which, in some instances, results in inadequate cooling of the passenger space or occupant space of the vehicle. Efforts have been made to provide two-speed input to a compressor of an air conditioning system with U.S. Pat. Nos. 2,807,147 issued Apr. 29, 1957 and 3,429,192 issued Feb. 25, 1969 relating particularly to such an arrangement. While the problem has been recognized and efforts made to provide an effective solution to such problem, the prior art does not provide an effective solution which is compact, easily installed on existing air conditioning compressors as well as new construction and effective for varying the compressor input drive speed inversely to the rotational speed of the crankshaft of the internal combution engine.